Equipment of this type is used, for example, in the pneumatic brake system of a railroad car. The prior art includes moisture removal devices such as those described in Japanese Utility Model Applications Nos. 55-23621 and 59-86231 in addition to Japanese Patent No. 53-34664, which will be explained in some detail hereinafter with respect to FIGS. 3, 4, and 5 of the drawings. In these Drawings, there is illustrated in FIG. 3 a general two-cylinder type of moisture removal apparatus. As shown therein, an air compressor designated CO and a cooler designated CL are provided. The inlet of the cooler CL is connected in fluid communication with an outlet of the air compressor CO. The outlet of the cooler CL is connected in f luid communication to an inlet of a drain valve designated DV. MV1 and MV2 designate a pair of solenoid valves having their flow inlets connected for fluid communication with the outlet of the drain valve DV. In this system, the solenoid valves MV1 and MV2 are switchable type valves. A pair of drying cylinders designated DR1 and DR2 are provided and have their inlet connected for fluid communication with the flow outlets of the solenoid valves MV1 and MV2. Each of the drying cylinders DR1 and DR2 contains an absorbent therein. Check valves designated CV1 and CV2 are connected in fluid communication with the outlets of the drying cylinders DR1 and DR2 in a manner such that the direction of this outlet of the drying cylinder is a reverse direction. Connected to the check valves CV1 and CV2 in parallel are throttle valves designated NV1 and NV2. SR designates a regenerated air reservoir connected to the throttle valves NV1 and NV2 and to the check valves CV1 and CV2. A second air reservoir designated MR is connected for fluid communication with the regenerated air reservoir SR through a check valve designated CV3. The check valve CV3 is connected such that the direction of the regenerated air reservoir SR is the reverse direction. Also provided is a governor designated GO for the air reservoir MR. The governor GO detects the pressure regulation upper limit value P2 and the lower limit value P1 (FIG. 5). In addition, the governor GO controls the air compressor CO and the drain valve DV. In this equipment, the solenoid valves MV1 and MV2 include an exhaust position designated (b) in which the flow outlet is opened to the atmosphere and the flow inlet is closed. This arrangement occurs when the apparatus is not energized or is off. Further, the solenoid valves MV1 and MV2 include a feed position designated (a) in which the exhaust outlet is closed and the flow inlet is connected to the flow outlet when the apparatus is energized or on.
When the solenoid valve MV1 is ON and the solenoid valve MV2 is OFF, the moist air from the air compressor CO is communicated to the drying cylinder DR1 through the cooler CL, the drain valve DV and the feed position (a) of the solenoid valve MV1. The moist air is dried by the absorbent in the drying cylinder DR1 and is then communicated to the regenerated air reservoir SR via the check valve CV1 and is thereafter communicated to the air reservoir MR via the check valve CV3. During this time, a portion of the dried air passing through the check valve CV1 is directed and flows in the reverse direction to the inlet from the outlet of the other drying cylinder DR2, through the throttle valve NV2, where it regenerates the absorbent in the drying cylinder DR2. During this regeneration of the absorbent in the drying cylinder DR2 the air becomes moist and is then exhausted from the system through the exhaust position (b) of the solenoid valve MV2. Now when the solenoid valve MV1 is switched to the OFF position and the solenoid valve MV2 is switched to the ON position, in reverse to the sequence described in detail above, the moist air is dried in the other drying cylinder DR2 and at the same time the absorbent is being regenerated in the other drying cylinder DR1. At the time the pressure in the air reservoir MR reaches the pressure regulation upper limit value P2 of the governor GO the air compressor CO is stopped and the drain valve DV opens to drain. Thereafter, when the pressure in the air reservoir MR reaches the pressure regulation lower limit value P1 of the governor GO, the drain valve DV closes thereby stopping draining and the air compressor CO goes into operation.
FIGS. 4 and 5 are graphs which illustrate over time the control process for switching the drying and regeneration of the above-described pair of prior art drying cylinders DR1 and DR2.
In one method of operation, according to the prior art and illustrated in FIG. 4, the solenoid valves MV1 and MV2 are always switched ON and OFF at each predetermined time T as determined by a timer which has not been illustrated in the drawings. In other words, one pair of drying cylinders DR1 and DR2 repeat the drying and regeneration cycles in alternation.
In a second method of operation according to the prior art and illustrated in FIG. 5, from which the table in FIG. 3 of the Japanese Patent No. 53-34664 was prepared, the ON/OFF operation of the governor GO which detects the pressure P in the air reservoir MR is linked to the operation and stopping of the air compressor CO. In this method of operation, when the air compressor CO is stopped, both solenoid valves MVl and MV2 go off and both drying cylinders DR1 and DR2 are switched to the regeneration status. In this method, when the air compressor CO is operated, the solenoid valves MV1 and MV2 are switched into the reverse status from the previous operating time interval and the drying and regeneration of the absorbent in the drying cylinders DR1 and DR2 can be switched.
One of the principal disadvantages associated with the above-described methods is that the switching mechanism which includes the solenoid valves MV1 and MV2 and their control portions become worn out rather quickly. This condition can cause increased damage to the overall pneumatic system. In particular, the first method repeats the drying and the regeneration of the absorbent in the drying cylinders DR1 and DR2 in alternation during each predetermined time T as controlled by the timer regardless of the operation or inoperation of the air compressor CO. Because it can be switched even though the air compressor CO is stopped, the frequency of switching is increased causing additional wear on the above-described components.